The present invention relates to a method for estimating the moment of inertia of the rotating unit of a washing machine, and to a washing machine implementing said method.
In particular, the present invention relates to a method that is able to estimate the moment of inertia in a washing machine or in a washing-and-drying machine of the type comprising: a box-like frame, and a washing unit set within the frame and comprising a tub fixed within the frame by means of a suspension equipment and a rotating unit, which is, in turn, provided with a laundry drum housed in an axially rotatable way within the tub, and a driving device able to set the laundry drum in rotation about its longitudinal axis inside the tub itself.
Methods are known that are able to determine the unbalancing of the washing unit of a washing machine in order to control the speed of rotation of the laundry drum so as to prevent possible conditions of collision of the washing unit with the frame and at the same time reduce vibrations and/or phenomena of bouncing of the washing machine caused by said unbalancing.
Some of the aforesaid methods determine the unbalancing of the washing unit through calculation of the moment of inertia of the “total rotating load” associated to the mass of the rotating unit plus the mass of the laundry housed inside the laundry drum.
In particular, the aforesaid methods calculate the moment of inertia via an energy-balance function, which necessarily requires both a measurement of the torque and a measurement of the speed of rotation of the laundry drum in a condition of “stability” of the rotating unit, which is reached only when, thanks to the centrifugal force, the laundry is substantially stuck to the internal wall of the laundry drum in a state of immobility.
If the energy-balance function used in the aforesaid methods on the one hand enables precise calculation of the moment of inertia of the rotating unit plus the laundry contained in the drum, on the other hand it is constrained to a condition of “stability” of the rotating unit being reached, which occurs when the speed of rotation of the washing drum reaches the so-called “sticking speed”, which, as is known, is the minimum speed of rotation of the drum at which the laundry remains completely stuck to the wall of the drum.
The sticking speed referred to above can reach relatively high values and consequently, in the case of non-uniform distribution of the laundry inside the drum, can determine an uncontrolled unbalancing of the rotating unit so causing a collision of the washing unit with the frame.
There consequently exists, on the one hand, the need to eliminate the risk of collision of the washing unit with the frame in any condition of operation of the washing machine and, on the other hand, the need to have available an estimate of the moment of inertia of the rotating unit plus laundry present in the laundry drum even when the speed of rotation is maintained around small values, i.e., lower than the sticking speed.